User Impersonation as a Service in End-to-End Testing
Boni García, Francisco Gortázar, Micael Gallego and Eduardo Jiménez
Universidad Rey Juan Carlos, Calle Tulipán S/N, 28933 Móstoles (Spain)
Keywords: End-to-End Testing, User Impersonation, Software as a Service, WebRTC.
Abstract: Testing large distributed heterogenous systems in cloud environments is a complex task. This situation
becomes especially difficult when carrying out end-to-end tests, in which the whole system is exercised,
typically through its graphical user interface (GUI) with impersonated users. These tests are typically
expensive to write and time consuming to run. This paper contributes to the solution of this problem by
proposing an open source framework called ElasTest, which can be seen as an elastic platform to carry out
end-to-end testing for different types of applications, including web and mobile. In particular, this piece or
research puts the accent on the capability to impersonate final users, presenting a real case study in which
end-to-end tests have been carried out to assess the correctness of real-time communications among
browsers using WebRTC.
1 INTRODUCTION
Modern software systems are increasingly complex.
Nowadays, architectures involving distributed
heterogenous services, cloud native, and
microservices are more and more common. As
usual, in order to accomplish a satisfactory level of
quality for these systems, different aspects need to
be addressed. First, the expectations of final users
need to be met. Using the classical definition of
Verification and Validation (V&V) by the
distinguished professor of computer science Barry
Boehm, this part is known as validation -are we
building the right product?- (Boehm, 1979). Second,
we need to ensure that the software meets its stated
functional and non-functional requirements, i.e., its
specification. This part is commonly known as
verification -are we building the product right?-.
Finally, we need to reduce the number of software
defects (commonly known as bugs) in our system to
the minimum, ideally to zero.
V&V include a wide array of activities, mainly
divided in two groups. On the one hand, software
testing (or simply testing) consists of observing a
sample of executions (test cases), and giving a
verdict on them. Hence, testing is an execution-
based activity, and for this reason, it is sometimes
called dynamic analysis. On the other hand, static
analysis is a form of V&V that does not require
execution of the software. Static analysis can work
directly with the source code, and also with
representation of the software, such as model of the
specification of design. Common forms of static
analysis include peer review or automated software
analysis. Regarding the later, this technique is
usually delivered as commercial or open source tools
and services, commonly known as lint or linter.
This paper is focused in software testing, which
is a broad term encompassing a wide spectrum of
different concepts. Depending on the size of the
System Under Test (SUT) and the scenario in which
it is exercised, testing can be carried out at different
levels. There is no universal classification for all the
different testing levels. Nevertheless, the following
levels are broadly accepted in the literature (García,
2017):
▪ Unit: individual program units are tested. Unit
tests typically focus on the functionality of
individual objects or methods.
▪ Integration: units are combined to create
composite components. Integration tests focus
on the interaction of different units.
▪ System: all of the components are integrated
and the system is tested as a whole. There is a
special type of system testing called end-to-
end testing. In this approach, the final user is
typically impersonated, that is, simulated
using automation techniques.
▪ Acceptance: final users decide whether or not
the system is ready to be deployed in the
García, B., Gortázar, F., Gallego, M. and Jiménez, E.
User Impersonation as a Service in End-to-End Testing.
DOI: 10.5220/0006752207070714
In Proceedings of the 6th International Conference on Model-Driven Engineering and Software Development (MODELSWARD 2018), pages 707-714
ISBN: 978-989-758-283-7
Copyright © 2018 by SCITEPRESS – Science and Technology Publications, Lda. All rights reserved
707

consumer environment. These tests can be
seen as functional testing performed at system
level by final users or customers.
The first three levels (unit, integration, and
system) are typically carried out during the
development phases of the software life cycle. These
tests are typically performed by different roles of
software engineers, i.e. programmers, testers,
Quality Assurance (QA) team, etc. The objective of
these tests is the verification of the system. On the
other side, the fourth level (acceptance) is a type of
user testing, in which potential or real users are
usually involved (validation). As illustrated in
Figure 1, the different tests levels are commonly
depicted as a pyramid, in which the base is the unit
tests (which in in theory are more numerous), while
the number of other tests (integration, system,
acceptance) is decreasing as long as we ascend to the
top. This idea of a pyramid for the different testing
levels was first proposed by Mike Cohn (Cohn,
2009).
Figure 1: Testing levels and its relationship with V&V.
The capability to automate of the different tests
levels has a direct impact on the project costs. Thus,
user testing (acceptance) is unlikely to be fully
automated, since the evaluation of the final
consumer always comprises some kind of human
intervention, and therefore this kind of tests can be
costly. Development testing, on the other side, can
and should be automated. Regarding top-level tests
-system and end-to-end-, these tests typically drive
an application through its user-interface, checking
that the application returns the expected results. This
approach works well in simple scenarios, but at the
end of the day these tests are prone to potential
problems, such as brittle logic, expensive to write,
and time consuming to run (Fowler, 2012). This
situation leads to the ice-cream cone anti-pattern, in
which manual tests -which should be a reduced
number on the top- increases its number more and
more, while the number of down-level automated
tests (integration and unit) is reduced (Scott, 2015).
This situation can become a real pain for
software practitioners in the common case that the
SUT is increasingly large and complex, such as
distributed heterogenous, microservices, or cloud
native systems. This kind of software systems
aggregates many different distributes components,
which are typically built and run applications based
on Infrastructure as a Service (IaaS) combined with
operation tools and services such as Continuous
Integration (CI), container engines, or service
orchestrators, to name a few.
This piece of this research contributes in the
domain of end-to-end test automation (i.e. system
tests in which the user is impersonated) for large
complex distributed applications in cloud
environments. To make easier this process for
software practitioners, we have created an open
source framework ElasTest. As we will discover,
this framework provides advance test capabilities to
ease the end-to-end tests process for different kind
of applications, including web and mobile.
Moreover, ElasTest provides the capability of
impersonate final users on web and mobile devices,
by extending the standard W3C WebDriver
recommendation (Stewart, 2017). This service has
been evolved into a fully Software as a Service
(SaaS) model so that developers do not need to take
into consideration problems related to computing
resources scheduling, software provisioning or
system scaling, providing a high-level test capability
which can be referred as User Impersonation as a
Service (UIaaS).
The remainder of this paper is structured as
follows. Section 2 provides a brief overview in the
state-of-the-art on end-to-end testing and user
impersonation. Section 3 provides a description of
the ElasTest framework. Then, section 4 provides
extra details of the ElasTest’s User Impersonation
Service (called EUS in the ElasTest jargon). In order
to validate our proposal, a case study has been
performed using a videoconferencing web system
built on the top of WebRTC. The description and
results of this case study are contained in section 5.
Finally, section 6 provides the conclusions, findings,
and future work of this piece of research.
2 BACKGROUND
Testing distributed and heterogeneous software
systems, running over interconnected mobile and
cloud based platforms, is particularly challenging.
To verify these systems, developers face with
different problems, including the difficulty to test
the system as a whole due to the number and
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diversity of individual components, the difficulty to
coordinate the test participants due to the distributed
nature of the system, or the difficulty to test the
components individually.
Recent research effort has tried to quantify the
current state of the practice of the testing automation
level for this kind of software systems. For instance,
Lima and Faria have conducted an exploratory
survey on testing distributed and heterogeneous
systems that was responded by 147 software testing
professionals that attended to two industry-oriented
software testing conferences (Lima, 2016). The
survey results confirm the existence of a significant
gap between the current and the desired status of test
automation for distributed heterogenous system, and
confirm and prioritize the relevance of test
automation features for these systems.
Many different contributions in the literature
aimed to improve the current state of the art in end-
to-end testing. For instance, the European
Commission funded H2020 project TRIANGLE
1
is
building a framework to help app developers and
device manufacturers in the evolving 5G sector to
test and benchmark new mobile applications in
Europe. This framework evaluates Quality of
Experience (QoE) and enable certification for new
mobile applications and devices (Cattoni, 2016).
Regarding web and mobile applications, the
main mechanisms used in the current state-of-the-art
for the functional testing of these applications
consists on impersonating a user through some kind
of GUI automation technology, being Selenium
2
the
most popular solution for web applications. In this
domain, Selenium WebDriver is capable of drive
automatically real browsers, such as Chrome,
Firefox, Opera, Edge, Safari, etc., using different
programming languages, such as Java, C#, Python,
Ruby, PHP, Perl, or JavaScript. To that aim,
Selenium WebDriver makes calls to the browser
using each browser’s native support for automation.
The language bindings provided by Selenium
WebDriver communicates with a browser-specific
binary which acts as a bridge with the browser. The
communication between the WebDriver script and
the driver binary is done with JSON messages over
HTTP using the so-called JSON Wire Protocol
(Bruns, 2009). This mechanism, originally proposed
by the Selenium team is being standardized in the
W3C WebDriver recommendation (Stewart, 2017).
The second major component of the Selenium
1
http://www.triangle-project.eu/
2
http://www.seleniumhq.org/
framework is called Selenium Grid. This component
allows remote execution of Selenium WebDriver on
distributed machines. The architecture of Selenium
Grid is composed by a group of nodes, each running
on different operating systems and with different
browsers. Then, a central piece called hub (also
known as Selenium Server) keeps a track of the
nodes and proxies requests to them using JSON
Wire Protocol/W3C WebDriver messages. This
capability is used by the Appium
3
project to drive
mobile devices. In Appium, instead of web
browsers, mobile devices are registered in a central
component called Appium Server. As depicted in
Figure 2, following the Selenium Grid approach, the
Appium Server is remotely controlled by means of
Wire Protocol/W3C WebDriver messages, typically
used by tests of scripts implementing the WebDriver
API (Shah, 2014).
Figure 2: Selenium/Appium high-level architecture.
3 ELASTEST: AN ELASTIC
PLATFORM TO EASE END-TO-
END TESTING
ElasTest
4
is an open source
5
framework aimed to
ease the end-to-end testing activities for different
types of distributed applications and services,
allowing developers and testers to assess their cloud
applications in an elastic, and integrated
environment. The proposed framework manages the
full testing lifecycle, deploying and monitoring the
SUT, executing the end-to-end tests and exposing
the results to software engineers and testers.
In this paper we focus on the ElasTest capability
to impersonate browsers and mobile devices. This
service has been designed following a SaaS model in
3
http://appium.io/
4
http://elastest.io/
5
https://github.com/elastest/
User Impersonation as a Service in End-to-End Testing
709

Figure 3: ElasTest architecture.
order to make transparent for the final user potential
problems related to computing resources scheduling,
software provisioning or system scaling.
In order to understand how EUS works, first we
need to review the overall architecture of ElasTest,
depicted in Figure 3. First of all, we find the ElasTest
Test Orchestration and Recommendation Manager
(ETM), which is the access point to the framework.
It orchestrates all other components exposing
different interfaces for consumers, such as a web
GUI, a command line interface, and also an interface
with a custom Jenkins plugin.
ElasTest follows a microservices approach, and
the component which is responsible for discovering
and operating the different services that ElasTest
make available to tests is called ElasTest Service
Manager (ESM). This component is based on the
Open Service Broker API (OSBA)
6
for discovering,
registering and unregistering services within the
platform. RabbitMQ
7
is used as messaging queue for
the events communication among the different
services.
One of the key aspects handled out of the box by
ElasTest is related with data management. During its
operation, ElasTest gathers different sources of data
6
https://www.openservicebrokerapi.org/
7
https://www.rabbitmq.com/
from test execution, including SUT logs, different
types metrics -including SUT resource consumption,
packet-loss in the network traffic, or node failures,
among others-, or custom files issued by services -
e.g. browser/mobile session recordings carried out
by EUS-. The component responsible for the
persistence layer is called ElasTest Data Manager
(EDM), and it has been built on the top of on
MySQL
8
as relational database, Elasticsearch
9
as
search engine, and Alluxio
10
as virtual distributed
storage system.
The ElasTest Instrumentation Manager (EIM)
provides the capability of instrumenting the SUT to
inject potential system failures like packet-loss,
network bandwidth adjustments to emulate real
conditions, CPU bursting, and node failures, to name
a few. To that aim, Beats
11
agents are installed
together with the SUT.
Finally, the ElasTest Platform Manager (EPM) is
the component responsible of isolating the ElasTest
services from the underlying infrastructure. The
supported cloud infrastructures are OpenStack
12
,
8
https://www.mysql.com/
9
https://www.elastic.co/
10
https://www.alluxio.org/
11
https://www.elastic.co/products/beats
12
https://www.openstack.org/
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710

Table 1: Extension to W3C WebDriver recommendation by ElasTest User Impersonation Service.
Method
Path
Description
POST
/session/{sessionId}/element/{elementId}/event
① Subscribe to a given event
within an element
GET
/session/{sessionId}/event/{subscriptionId}
② Read the value of event for a
given subscription
DELETE
/session/{sessionId}/event/{subscriptionId}
③ Remove a subscription
GET
/session/{sessionId}/vnc
④ Get remote session
DELETE
/session/{sessionId}/vnc
⑤ Delete remote session
POST
/session/{sessionId}/usermedia
⑥ Set user media for WebRTC
GET
/session/{sessionId}/stats
⑦ Read the WebRTC stats
POST
/session/{sessionId}/element/{elementId}/latency
⑧ Measure end-to-end latency
of a WebRTC session
POST
/session/{sessionId}/element/{elementId}/quality
⑨Measure quality of a WebRTC
session
Amazon Web Services
13
(AWS), Docker
14
and
Kubernetes
15
. Moreover, Open Baton
16
is used for
orchestrating the SUT and the network services
within the ElasTest platform (Carella, 2015).
4 USER IMPERSONATION AS A
SERVICE
As introduced in section 2, testers’ need for user
impersonation is more and more demanded. For that
reason, nowadays there are several companies that
are growing business models basing on exposing
these capabilities through SaaS models, such as
Saucelabs
17
or BrowserStack
18
. However, these
solutions have relevant limitations. On the one hand,
these services have very relevant costs, which limit
their applicability for many projects. On the other
hand, these services only impersonate the user from
the perspective of its outgoing actions, but not from
the perspective of its incoming perceived QoE.
ElasTest progresses beyond the current state of
the art providing an advanced user impersonation as
a service capability that provides GUI automation
basing on open source paradigms and enables also
the evaluation of the perceived quality of users on
relevant scenarios such as real-time multimedia
applications. As introduced in the section before,
this feature has been implemented in the component
called ElasTest User Impersonation Service (EUS),
13
https://aws.amazon.com/
14
https://www.docker.com/
15
https://kubernetes.io/
16
https://openbaton.github.io/
17
https://saucelabs.com/
18
https://www.browserstack.com/
providing what we can call User Impersonation as a
Service (UIaaS). This service is devoted to provide
user impersonation for two types of user interfaces,
i.e. web browsers and mobile devices.
In order to expose this capability through an API
in a universal way, EUS has been implemented as an
extension of the W3C WebDriver API. As presented
in section 2, this recommendation is used to drive
remote browsers and mobile devices, by means of a
client-server technology implemented by Selenium
and Appium respectively. The vision of EUS is to
enhance the current support with additional advance
capabilities in a seamless and integrated solution.
To that aim, EUS exposes a REST API based on
JSON messages
19
which complements the W3C
WebDriver specification. The definition to this
REST API has been defined using Open API
notation
20
, and it is summarized in Table 1. In this
table, the first operation allows to subscribe to
events in a given element of the user interface. Then,
second operation allows to read the value for a given
subscription, and the third one allows to unsubscribe
to that event. Operations 4 and 5 are related with the
capability of remote GUI, provided by EUS out of
the box by means of Virtual Network Computing
(VNC). Using these commands, EUS allows to
watch in real-time the use of a browser or mobile
device, typically driven by a test script using the
WebDriver API.
The last group of operations summarized in Table
1 are targeted for WebRTC applications. WebRTC is
the umbrella term for a number of emerging
technologies that extends the web browsing model to
exchange real-time media with other browsers
(Loreto, 2017). Market momentum around WebRTC
19
http://elastest.io/docs/api/eus/
20
https://www.openapis.org/
User Impersonation as a Service in End-to-End Testing
711

is growing very fast nowadays, and therefore, it is
imperative for software testers to have a strategy in
place in order to assess WebRTC applications
efficiently. Nevertheless, testing WebRTC-based
applications in a consistently automated fashion is a
challenging problem. EUS contributes to the
solution of this problem with proving advance
features aimed to asses this kind of applications.
First of all, thanks to operation 6 presented in
Table 1, the EUS is capable of faking the user media
-video and/or audio- employed in a WebRTC
communication with a custom video/audio file
chosen by the tester. Then the operation 7, allows to
read all the collection of WebRTC stats, which is a
good indicator on Quality of Service (QoS) for
WebRTC. These include traffic metrics such as
network latency, network packet loss, network jitter,
retransmissions, or consumed bandwidth.
Moreover, EUS enables to measure the end-
user's perceived quality so that testing through the
validation of the subjective perceived quality. To
that, EUS analyses the multimedia QoE for audio
and video using different full-reference algorithms,
such as PESQ (Rix, 2001) for audio or SSIM (Wang,
2004) for video. Full-reference is type of QoE
media-based algorithms, in which the degraded
signal is compared with the original signal
(Chikkerur, 2011). This, applied to EUS, means that
a couple of browsers (or mobile devices) are needed,
first one acting as media source and the other acting
as media consumer. Internally, this process reuses
the aforementioned publish-subscribe mechanism, in
which quality events - audio or video- are published
periodically.
Finally, EUS provides several extra capabilities
in conjunction with the rest of ElasTest components.
On the one hand, it records every session in a
seekable recording, stored in EDM as a video file.
This feature improves the traceability of tests,
allowing users to check the evolution of test
executions when required. On the other hand, EUS
always gathers automatically the browser logs in
every session. Again, this information is stored
together the recording on EDM, and it can be a
valuable source of information for developers and
testers to try to trace the source of faults when tests
are failing.
EUS has been implemented as a Spring Boot
21
REST service listening for the enhanced version of
W3C WebDriver specification just presented. The
EUS workflow starts with the invocation of a
21
https://projects.spring.io/spring-boot/
session creation carried out in a WebDriver script.
Once the EUS controller receives this message
(POST /session), proxies the message to a
Selenium/Appium server provided on demand by
EPM. Once the browser or mobile device is
available, a unique session identifier (sessionId,
which is always available in the operations described
in Table 1) is sent as response. This parameter is used
in successive requests to interact with the
browser/mobile just created. At the end of the
session, the script will invoke the termination
command (DELETE /session) using the proper
session identifier. At this point, the infrastructure
resources are released by EPM, and the complete
recording a logging data is sent to EDM.
5 CASE STUDY: TESTING
WEBRTC APPLICATIONS
MADE WITH OPENVIDU
In order to validate our proposal, a case study
focused on WebRTC applications have been carried
out. Concretely, we have cooperated with the team
developing the project OpenVidu
22
, an open source
videoconferencing WebRTC framework. OpenVidu
follows a client-server architecture and therefore is
made up by two main components. On the client-
side, the OpenVidu Browser is a JavaScript/
TypeScript library which allows to create video
calls, join users to them, and send/receive media
streams. On the server-side, the OpenVidu Server
receives the operations from clients establishing and
managing the video-calls.
In order to carry out end-to-end tests of WebRTC
applications, it is mandatory to use browsers that
implements the WebRTC stack, such as Chrome or
Firefox. For that reason, in the OpenVidu project,
end-to-end tests have been implemented using
Selenium WebDriver. In the testing process carried
out by the OpenVidu team, these tests were executed
in a Jenkins Continuous Integration server. In this
server the latest versions of Chrome and Firefox
were installed, and Selenium sessions were executed
through a virtual framebuffer display server -Xvfb-.
The research question driving this case study is
the following: “Is the ElasTest user impersonation
service capable of improving the end-to-end testing
process within the OpenVidu project?”. To address
this question, first an instance of ElasTest was
22
http://openvidu.io/
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Figure 4: Screenshot of ETM/EUS during the execution of a OpenVidu end-to-end test.
provided to the OpenVidu team. The idea was to
reuse the existing tests, adapting them to be executed
inside ElasTest.
Due to the fact that the existing test suite was
based on Selenium WebDriver, few changes was
required in the test logic. The existing codebase was
implemented in Java, and therefore the required
change was related to the specific objects to control
browsers -i.e. ChromDriver for Chrome and
FirefoxDriver for Firefox-, by remote browser
drivers, called RemoteDriver in Java. These
objects require the URL to connect with the
Selenium Server, which is implemented in ElasTest
by EUS. When tests are executed inside ElasTest,
this URL is available by reading the environmental
variable ET_EUS_API. The source code of these
tests is available on GitHub
23
.
The SUT lifecycle was managed by ElasTest
together with the test execution. In this case study, a
Docker Compose
24
script was configured within the
ETM, defining the OpenVidu application under test
and its dependencies. Figure 4 provides an ETM
screenshot of the exectution of one end-to-end test
against the SUT while it is executed by the EUS. As
explained in the section before, once the test
23
https://github.com/elastest/demo-projects
24
https://docs.docker.com/compose/
finished, a recording of the session navigation,
together the the browser logs is stored persistenly in
ElasTest.
Once the tests were adapted and executed in
ElasTest, we were able to draw some conclusions
about the UIaaS. First of all, we conclude that the
fact that EUS is based on the W3C WebDriver
standard, facilitates its adoption in an existing test
codebase. Second, the capability to provide different
types of browsers and version in a semanless and
elastic manner is very valuable for testers, since it
avoids to manage directly the infrastructure reducing
the efforts required mainly in DevOps side, and
providing valuable assets to create compatibity tests
for testers. Finally, the capability for storing to the
browser session recording and logging makes a big
difference for OpenVidu testers. This feature allows
to trace and debug failed tests in a much more
realiable way than before, in which testers were
blind to trace errors of tests executions on their
Jenkins infrastructure.
6 CONCLUSIONS AND FUTURE
WORK
Software testing is the most commonly performed
activity within V&V. Modern web and mobile
applications are characterized by rapid development
User Impersonation as a Service in End-to-End Testing
713

cycles, which supposes that testers tend to pay scant
attention to automated end-to-end test suites. As a
result, this kind of tests is usually abandoned or
poorly performed.
This paper introduces ElasTest, an open source
platform aimed to ease end-to-end tests for
heterogenous large distributed systems. The mision
of ElasTest is to make easier the developers’ life. To
that aim, among other capabilities, ElasTest
implements what we can call User Impersonation as
a Service (UIaaS). This service enables the
impersonation of end-users’ in their tests through
GUI instrumentation. This service provides full
compatibility with external browser/mobile drivers,
but enhanced with extra capabilities, such as event
subscription, log gathering, or advance media
capabilities for WebRTC applications. This service
have be built extending the W3C WebDriver
specification, and therefore, popular technologies
such as Selenium and Appium are completely
compatible with ElasTest.
At the moment of this writing, ElasTest is still in
its infancy. Therefore, some features are still under
development. For instance, the measurent of the end-
users’ perceived QoE is still ongoing. Measuring
QoE is in general a complex topic and this task shall
perform the appropriate research activities for
evaluating the most suitable way of doing it, which
may involve simple mechanisms such as evaluation
of response-time from the GUI.
ACKNOWLEDGEMENTS
This work has been supported by the European
Commission under projects NUBOMEDIA (FP7-
ICT-2013-1.6, GA-610576), and ElasTest (H2020-
ICT-10-2016, GA-731535); by the Regional
Government of Madrid (CM) under project
Cloud4BigData (S2013/ICE-2894) cofunded by FSE
& FEDER; and Spanish Government under project
LERNIM (RTC-2016-4674-7) cofunded by the
Ministry of Economy and Competitiveness, FEDER
& AEI.
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